The propagation of inverted Neel wall sections in a serial accessed memory system was first proposed by L. J. Schwee in the publication "Proposal On Cross-Tie Wall and Bloch-Line Propagation in Thin Magnetic Films", IEEE Transactions on Magnetics, MAG 8, No. 3, pages 405-407, September 1972. Such memory systems utilizes a ferromagnetic film strip of approximately 81% Ni-19% Fe approximately 350 Angstroms (A) thick in which cross-tie walls can be changed to Neel walls and Neel walls can be changed to cross-tie walls by applying appropriate drive fields thereto. Associated with a cross-tie wall is a section of an inverted Neel wall that is bounded by a cross-tie on one end and a Bloch-line on the other end.
In such a cross-tie wall memory system, information is entered at one end of the serial access memory system by the generation of an inverted Neel wall section, formed by a cross-tie on one end and a Bloch-line on the other, that is representative of a stored binary 1 or of a non-inverted Neel wall section (i.e., the absence of a cross-tie, Bloch-line pair) that is representative of a stored binary 0. Such information is moved or propagated along the cross-tie wall by the successive generation (and then the selective annihilation) of inverted Neel wall sections at successive memory cells along the cross-tie wall. In the D. S. Lo, et al, U.S. Pat. No. 3,906,466 there is disclosed a propagation circuit for the transfer of inverted Neel wall sections through successive memory cells along a cross-tie wall. In the L. J. Schwee, et al, AIP Conference Proceedings, No. 29, 21st Annual Conference on Magnetism and Magnetic Materials, 1975 published April, 1976, pages 624-625 and in the publication "Geometry of Serrated Magnetic Film Strips for the Cross-Tie Memory" D. S. Lo, et al, IEEE Transactions on Magnetics, January 1977, pages 936-938, there have been published some recent results of the further development of cross-tie wall memory systems.
In a cross-tie wall memory system, the selective generation and propagation of the digital-data-representing inverted Neel wall sections and the associated cross-tie, Bloch-line pairs have been demonstrated in the laboratory. Additionally, it has been shown that the data track of a cross-tie wall memory system may be configured into a film strip having repetitive patterns of asymmetrically serrated edge contours. Such film strip configurations are disclosed in the L. H. Johnson, et al, U.S. Pat. No. 4,075,612 the L. J. Schwee, et al, U.S. Pat. No. 4,100,609, the L. J. Schwee, et al, U.S. Pat. No. 4,192,012, and in the publication "Cross-Tie Memories Simplified by the Use of Serrated Strips", L. J. Schwee, et al, AIP Conference Proceedings, No. 29, 21st Annual Conference on Magnetism and Magnetic Materials, 1975, published April, 1976, pages 624-625.
More recently, it has been proposed to construct cross-tie wall memory systems from a plurality of data tracks, each of which is formed as a strip of isotropic magnetic film, i.e., a film having substantially zero uniaxial anisotropy. The data-track-defining strip of isotropic magnetic film utilizes its shape, i.e., its edge contour, induced anisotropy, rather than its easy access magnetic field induced anisotropy, to constrain the cross-tie wall within the planar contour of the film strip. The use of the shape induced anisotropy of an isotropic strip of magnetic film permits the use of nonlinear, i.e., curved, data tracks that may be configured into cross-tie wall memory systems that perform both memory and logic functions. Such a system is disclosed in the E. J. Torok U.S. Pat. No. 4,075,613.
Although the generation, propagation and logic manipulation of the inverted Neel wall section-defining-data-bits and the detection and readout thereof have been receiving considerable study, one area that can still use improvement in the development of a cross-tie wall memory system is the data track or the device that stores and structures the information, i.e., the cross-tie, Bloch-line pairs, in the cross-tie wall memory system. In the copending patent application of G. J. Cosimini, et al, Ser. No. 218,993 filed Dec. 22, 1980, there is disclosed such an improved data track. This improvement consists of the addition of areas of decreased data track thickness along the geometric centerline of the data track for forming energy wells that provide an increased cross-tie, Bloch-line pair resistance to deleterious movement away from the geometric centerline of the data track and/or along the cross-tie wall. Energy wells, for storing the cross-ties, are formed between apposing necks, or across the narrow portions of the data track and transverse the data track centerline, for producing magnetostatically favorable positions for the cross-tie thereat. These energy wells provide an increased resistance to the creep or movement of the cross-tie wall, and the associated cross-tie, Bloch-line pairs, when subjected to repetitive memory drive field cycling during memory operation. The present invention is directed toward an improved method and an apparatus for storing and structuring the information in a cross-tie wall memory system.